Switch contact and method of making the same



Nov. 14,1933. A. T. MUSGRAVE; 1,935,516

SWITCH CONTACT AND METHOD OF MAKING THE SAME Filed April 15, 1950Patented Nov. 14, 1933 UNITED STATES PATENT OFFICE swrrcn CONTACT ANDMETHOD or MAKING THE SAME Arthur T. Musgrave, Grecnsburg, Pa., assignorto Railway and Industrial Engineering Company,

Greensburg, Pa., a corporation of Pennsylvania Application April 15,1930. Serial No. 444,579

9 Claims. (01. 29-15555) 6 It had been the practice to provide a largecontact area between the switch blade and theswitch jaws when the switchwas to carry relatively heavy currents, the practice having been toprovide such contact areas that the current density was of the order of50 to 80 amperes per square inch when the unit pressure between thecontact surfaces was a few pounds per square inch. The copendingapplication of Carl G. Koppitz, Ser. No. 367,013, filed May 29, 1929,describes an electrical switch in which the contact surface is of verylimited extent and the unit pressure is of the order of upward of manythousand pounds per square inch. As described in the said application,switches of this type 'may be made by drilling the switch blade orswitch jaw and inserting therein a section of a harder metal whichextends beyond the original surface of the blade or jaw.

An object of the present invention is to prcvide switch elements inwhich contact surfaces of limited area are integral with the main bodyof the element but have electrical and metallurgical characteristicsdiffering from those of the element. elements having limited contactareas that are integral with but harder than the metal forming theremainder of the elements. A further object is to provide a switchelement in which a small portion of the metal of the element is forcedoutwardly from the original surface of the ele ment by the pressureapplied upon and at an angle to the said surface.

Other objects of the invention are to provide methods of forming contactelements having the characteristics noted above. Other specific objectsare to provide methods of forming switch contact elements having limitedareas forced outwardly beyond the original surface of the element.

These and other objects of the invention will be apparent from thefollowing specification when taken with the accompanying drawing inwhich:

Fig. 1 is a fragmentary side elevation of a disconnect switch,

50 Fig. 2 is an end elevation of the same,

i Fig. 3 is an enlarged side elevation of the end of a switch bladehaving a limited contact area formed thereon,

Fig. 4 is a transverse section through the said contact area,

Another object is to provide switch Figs. 5 and 6 are fragmentarysectional views illustrating the method of stamping a switch element toprovide limited contact areas thereon,

Fig. 7 is a fragmentary sectional view of a spinning tool for forming alimited contact area, 6 and,

Fig. 8 is an end elevation of the spinning tool.

In the drawing, the reference numerals 1 indicate'the ends of theinsulator columns or other supports upon which the disconnect switch is85 mounted. The lower support 1 carries a suitable fitting 2 upon whichthe switch blade or blades 3 are povitally mounted, the fitting beingprovided with an integral terminal lug 4. The upper insulator columncarries a fitting 5 which has an integral terminal lug 6 and a pluralityof substantially parallel blades '7 to provide the switch jaw withinwhich the switch blade 3 may be engaged.

As best shown in Fig. 2, the switch blades 3 do not have full surfacecontact with the transversely alined portions of the adjacent blades 7of the switch jaw, but the engagement is limited to the domes orspherical bosses 8 that are formed on the switch blades. bosses 8 atopposite sides of 'the switch blade may be, and preferably are, in axialalignment with each other.

Although it would be possible to form an element having the identicalshape as the described blade element 3 by casting an oversized elementand grinding to final form, or by machining away the excess metal from alarger blank, such operations would be comparatively expensive, andwould not impart to the elements the mechanical properties which areessential when small contact areas are to slide along plain contactsurfaces under heavy pressure. As shown graphically in Figs. 5 and 6,the contact bosses may be formed on the surface of the contact elementor blade 3 by stamping the blade between dies 9 that have conicalrecesses 10 in the adjacent ends thereof. When the dies are pressedtoward each other and into the metal forming the blade 3, pressure isexerted over an annular area and, due to the inclined end faces 10 ofthe dies, the lines of application of the pressure define the surface ofa pair of cones that have their bases located beneath the surface of theswitch-blade. sure along converging lines effects a cold flow of themetal toward the center of the annular area, and the central portion ofthis area is forced outwardly beyond the planes defining the parallelsurfaces of the contact element 3.

As shown in Fig. 4, the o This application of pres rollers 13.

Similar spherical bosses may be formed by spinning tools of the generaltype shown in Fig. 8. The tool may take the form of a cylindrical rod 11having a central extension 12 which provides seats for the inner ends ofthe pivots of the conical The -pivotal supports for the outer ends ofthe series of rollers are mounted in a sleeve 14 that telescopes overthe end of therod 11.

The blade 3 will preferably be formed of soft copper of high electricaland thermal conductivity and the jaw members 7 are preferably of aharder metal such as spring copper. The normal spacing of the jawmembers '7 is slightly less than the maximum thickness of the switchblades 3 in order that there may be a relatively low pressure betweenthe engaging surfaces. Although the total pressure may be comparativelylow, for example, of the order of from 25 to '70 or 80 pounds, the unitpressure of contact is extremely high since switch elements engage theareas which are of the order of point contacts, i, e., the area inengagement at each contact is of the order of one one-hundredth of onesquare inch.

The switch shown in Figs. 1 and 2 provides eight contact areas and Ihave found that a switch of this type will carry loads of the order of2000 amperes and upward. Assuming an equal distribution of the current,each contact area carries approximately 250 amperes, and therefore thecurrent density is of the order of 25,000 amperes per square inch. Theoperation of a switch of this limited contact area type is materiallyimproved when the contact points or zones are provided by an integralpart of the metal of the blade.

The separate contact inserts give rise to electrical and thermal lossesat the junction of the metals and such losses are reduced orsubstantially eliminated when the contact area is formed by pressing ordeforming the metal of the blade to force a part of the metal out fromthe original surface of the blade. It is to be noted that the contactelements embodying the invention possess the same advantages as thoseformed by separate inserts so far as concerns the relative hardness, andthe electrical and thermal conductivity of the body of the contactelement and the contact bosses. The cold working of a soft copper switchblade results in a hardening of the worked section, thus providing ahardened contact area of limited extent, but the remainder of the bladeor switch element has a high electrical and thermal conductivity.

The opposed contact bosses are preferably alined in a single planepassing through the axis of the movable element. This constructionprovides the full contact area and contact pressure as soon asengagement of the line of bosses with the other contact element iscomplete and therefore, aside from any arcing conduction upon theopening of the switch, the effective opening or closing of the switchcorresponds to a very small relative movement of the cooperating contactmembers.

It will be apparent that the invention is not limited to the formationof the contact-restricting area or areas upon the movable element of ahigh pressure contact switch since the same economy in manufacture andthe same advantages in operation are observed when the projecting bossesare located on the switch jaw.

While I have described two methods of swaging or upsetting a part of themetal, it will be apparent that other methods may be employed to efiectthe desired outward flow of the metal at opposed zones on opposite facesof the contact element.

The spherical boss may be replaced by bosses or projecting areas ofother contour and, when extremely heavy currents are to be carried, itmay be convenient to provide a line contact in place of a plurality ofpoint contacts. The deforma tion of the metal to provide a line contactmay be efiected by applying pressure along two converging planes.

It will be apparent that the invention is not limited to disconnectswitches of the high pressure contact type, since it may be usefullyemployed for all switches that carry heavy currents. The particular datagiven above is illustrative of the invention, but it is to be understoodthat the invention is not limited to switches employing unit pressuresor current densities of the exact or approximate values hereinspecified.

I claim:

1. The method of forming contact area of limited extent on the surfaceof a switch contact element, which comprises applying pressure to theperiphery of a limited area of said elemnt to effect a cold flow of themetal of said limited area towards the center thereof, whereby the metalat the center of said limited area is forced outwardly from the originalsurface of said element.

2. The invention as set forth in claim 1, wherein the pressure issymmetrically applied at opposite surfaces of said element, wherebyraised contact surfaces are formed at transversely alined points on saidelement.

3. The method of forming a contact area of limited extent upon a switchcontact element, which comprises applying pressure upon the sur= face ofsaid element along spaced converging lines, whereby the metal betweensaid lines of application is forced outwardly from the surface of saidelement.

i. The method as set forth in claim 4, wherein the converging linesalong which pressure is applied define the surface of a cone whose apexlies outside said element.

5. In the manufacture of a switch element for a high pressure contactswitch of high currentcarrying capacity, the process which comprisesshaping a restricted section of a one-piece element to form a contactarea projecting beyond the surface of the adjacent portion of saidelement, and hardening the surface of said contact area to impart acharacteristic thereto which differs from a corresponding characteristicof the adjacent portion of said element.

6. In the manufacture of a switch element for a high pressure contactswitch of high currentcarrying capacity, the process which comprisescold working a restricted portion of a one-piece element to impartthereto a rounded and smooth contact surface and simultaneouslyhardening said rounded contact surface to impart thereto electrical andmechanical characteristics different from those of the remainder of thesaid one-piece element.

'7. In the manufacture of a switch element consisting of a metallicplate of one density and a contact boss integral with and projectingbeyond said plate, the method which comprises simultaneously hardening asection of said plate and forcing the said hardened section outwardly toform a contact boss by applying pressure to the periphery of saidsection to force the same below the surface of said plate and towardsthe center of said. Section.

construction 01' a switch, said element comprising a flat plate formedof relatively soft metal of high electrical and thermal conductivity,and a contact boss integral with and projecting beyond one face of saidplate, the metal of said boa being harder than that of said plate andpossesslnz a lower thermal and electrical conductivity.

AR'I'HUR T. MUSGRAVE.

